A buddy of mine just went through two 753s. He said the sound was great, but there were a few issues with both of them. He said the remote would not learn new commands, both had some random crackling/popping, and the video out on one was pixellated.
I haven't used the 5500 yet, but I recently installed a 5400 for a customer. As long as your room isn't huge and you don't have low impedance speakers, the 5500 should be a solid performer. It's a rare case that Marantz actually has more features, but in this case, the 5500 does have some things like MRAC that might be useful.
Soundwise and probably power wise, I think the 753 would be better, but overall, the 5500 is probably a better choice.
BTW, you might check the Deals area here. I posted a link to a deal for a NEW 7400 for $629 from an authorized dealer.
